Any big cat from the genus Panthera, like lion, tiger, leopard and jaguar, is called Panther; black panther is the common name for a black specimen (a melanistic variant) of any of several species of these cats.
The term panther is generally refered to leopards, but in North America is related to pumas and in Latin America to jaguars.

Melanism is most common in jaguars (Panthera onca) - where it is due to a dominant gene mutation - and leopards (Panthera pardus) - where it is due to a recessive gene mutation. Close examination of one of these black cats will show that the typical markings are still there, and are simply hidden by the surplus of the black pigment melanin. Cats with melanism can co-exist with litter mates that do not have this condition. In cats that hunt mainly at night the condition is not detrimental. White panthers also exist, these being albino or leucistic individuals of the same three species.

It is probable that melanism is a favorable evolutionary mutation with a selective advantage under certain conditions for its possessor, since it is more commonly found in regions of dense forest, where light levels are lower. Melanism can also be linked to beneficial mutations in the immune system.

-From Wikipedia

It's the most common panther.
The spotted pattern is still visible, especially from certain angles where the effect is that of printed silk. Skin color is a mixture of blue black gray and purple with rosettes.
The mutation is recessive and some spotted leopards can produce black cubs (if both parents carry the gene in hidden form) while black leopards always breed true when mated together.
The black leopard is able to hunt and kill animals outweighing them by more than 1,350 pounds but this is rare because of competition from tigers and lions.
Black leopards are reported from most densely-forested areas in south-western China, Burma, Assam and Nepal; from Travancore and other parts of southern India and are said to be common in Java and the southern part of the Malay Peninsula where they may be more numerous than spotted leopards. They are less common in tropical Africa, but have been reported from Ethiopia (formerly Abyssinia), the forests of Mount Kenya and the Aberdares. One was recorded by Peter Turnbull-Kemp in the equatorial forest of Cameroon.

-From Wikipedia